Changes in platelet monoamine oxidase activity, cholesterol levels and hyperactive behaviour in adolescents over a period of three years

Peripheral biomarkers of attention-deficit hyperactivity disorder: Current status and future perspective

Attention-deficit hyperactivity disorder (ADHD) is one of the most common neurodevelopmental disorders, characterized by a persistent pattern of inattention, hyperactivity, and impulsivity. Since the diagnosis of ADHD is defined by operational diagnostic criteria consisting of several clinical symptoms, a number of heterogeneous mechanisms have been considered to be implicated in its pathophysiology. Although no clinically reliable biomarkers are available for the diagnosis of ADHD, several plausible candidate biomarkers have been proposed based on recent advances in biochemistry and molecular biology. This review article summarizes potential peripheral biomarkers associated with ADHD, mainly from recently published case-control studies. These include 1) biochemical markers: neurotransmitters and their receptors, neurotrophic factors, serum electrolytes, and inflammation markers; 2) genetic and epigenetic markers: microRNA, mRNA expression, and peripheral DNA methylation; 3) physiological markers: eye movement and electroencephalography. It also discusses the limitations and future directions of these potential biomarkers for application in clinical practice.

Risk factors for steroid-induced adverse psychological reactions and sleep problems in pediatric acute lymphoblastic leukemia: A systematic review

OBJECTIVE

Steroids play an essential role in treating pediatric acute lymphoblastic leukemia (ALL). The downside is that these drugs can cause severe side effects, such as adverse psychological reactions (APRs) and sleep problems, which can compromise health-related quality of life. This study aimed to systematically review literature to identify risk factors for steroid-induced APRs and sleep problems in children with ALL.

METHODS

A systematic search was performed in six databases. Titles/abstracts were independently screened by two researchers. Data from each included study was extracted based on predefined items. Risk of bias and level of evidence were assessed, using the Quality in Prognosis Studies tool and the Grading of Recommendations Assessment, Development and Evaluation tool, respectively.

RESULTS

Twenty-four articles were included. APR measurement ranged from validated questionnaires to retrospective record retrieval, sleep measurement included questionnaires or actigraphy. Overall, quality of evidence was very low. Current evidence suggests that type/dose of steroid is not related to APRs, but might be to sleep problems. Younger patients seem at risk for behavior problems and older patients for sleep problems. No studies describing parental stress or medical history were identified. Genetic susceptibility associations remain to be replicated.

CONCLUSIONS

Based on the current evidence, conclusions about risk factors for steroid-induced adverse psychological reactions or sleep problems in children with ALL should be drawn cautiously, since quality of evidence is low and methods of measurement are largely heterogeneous. A standardized registration of steroid-induced APRs/sleep problems and risk factors is warranted for further studies in children with ALL.

Platelet MAO activity and COMT Val158Met genotype interaction predicts visual working memory updating efficiency

The exact mechanism how serotonergic and dopaminergic systems relate to one another in working memory (WM) updating is unknown. Platelet monoamine oxidase (MAO) has been used as a marker for central serotonergic capacity, and catechol-O-methyltransferase (COMT) as a marker for central dopaminergic capacity. This study aimed to describe the interaction of platelet MAO activity and COMT Val158Met genotype in visual working memory updating: the ability to replace old information with new within hundreds of milliseconds. Previous studies suggest that platelet MAO activity and COMT Val158Met genotype could have an interaction effect on working memory. However, there are no studies that have directly examined the interaction of these biomarkers in WM updating. We used a 2-back updating task with facial expressions and defined updating efficiency as response times for correct responses. 455 subjects from a population representative sample were included. Mixed models were used for data analysis with an aim to study the interaction of COMT Val158Met genotype (Val/Val, Val/Met and Met/Met) and the level of MAO activity (high vs low). Education, IQ, sex, simple reaction times, and overall updating accuracy were included as covariates. We found that the effect of COMT Val158Met on updating efficiency depends on the level of platelet MAO activity. Low MAO in contrast to high MAO was associated with an increase in updating efficiency in Val/Met but a decrease in Met/Met. The results are discussed in the context of serotonin and dopamine functions in brain regions related to WM. The findings support the view that serotonin modulates dopaminergic activation in updating and contribute to understanding the role of serotonin in PFC, top-down inhibitory signals, and its interactions with dopamine in WM processes.

A systematic review and meta-analysis examining the interrelationships between chemical and non-chemical stressors and inherent characteristics in children with ADHD

Children may be more vulnerable to the combined interactions of chemical and non-chemical stressors from their built, natural, and social environments when compared to adults. Attention deficit/hyperactivity disorder (ADHD) is the most commonly diagnosed childhood neurodevelopmental disorder and is considered a major public health issue, as 75% of childhood cases persist into adulthood. ADHD is characterized by developmentally inappropriate levels of hyperactivity, impulsivity, and inattention, with the neurotransmitter serotonin regulating these symptoms. Monoamine oxidase A (MAOA) aids in serotonin uptake and is often implicated in behavioral and emotional disorders, including ADHD. When children are exposed to cigarette smoke, bisphenol A (BPA), or organophosphate pesticides, MAOA activity is inhibited. Non-chemical stressors, such as traumatic childhood experiences, and lifestyle factors, complicate the relationship between genotype and exposures to chemical stressors. But the co-occurrence among outcomes between exposures to chemical stressors, non-chemical stressors, and the low activity MAOA genotype suggest that mental illness in children may be influenced by multiple interacting factors. In this systematic review, we examine the existing literature that combines exposures to chemical and non-chemical stressors (specifically childhood trauma), MAOA characteristics, and ADHD diagnosis to investigate the interrelationships present. We observe that chemical (lead [Pb], phthalates/plasticizers, persistent organic pollutants, and cigarette smoke) exposure is significantly related to ADHD in children. We also observed that existing literature examining the interaction between MAOA, exposures to chemical stressors, and traumatic experiences and their effect on ADHD outcomes is sparse. We recommend that future studies investigating childhood ADHD include chemical and non-chemical stressors and inherent characteristics to gain a holistic understanding of childhood mental health outcomes.

The role of MAO in personality and drug use

Monoamine oxidases, both MAO-A and MAO-B, have been implicated in personality traits and complex behaviour, including drug use. Findings supporting the involvement of MAO-A and MAO-B in shaping personality and in the development of strategies of making behavioural choices come from a variety of studies that have examined either prevalence of gene variants in clinical groups or population-derived samples, estimates of enzyme activity in blood or, by positron emission tomography, in the brain and, most recently, measurement of methylation of the gene. Most of the studies converge in associating MAO-A and MAO-B with impulsive, aggressive or antisocial personality traits or behaviours, including alcohol-related problems, and for MAO-A available evidence strongly supports interaction with adverse environmental exposures in childhood. What is known about genotype effects, and on expression and activity of the enzyme in the brain and in blood has not yet been possible to unite into a mechanistic model of the role of monoamine systems, but the reason for this low degree of generalization is likely caused by the cross-sectional nature of investigation that has not incorporated the developmental effects of MAO-s in critical time windows, including the foetal period. The "risk variants" of both MAO-s appear to increase behavioural plasticity, as supportive environments may particularly well enhance the hidden potential of their carriers. Importantly, male and female brain and behaviours have been found very different with regard to MAO×life events interaction. Future studies need to take into consideration these developmental aspects and sex/gender, as well as to specify the role of different types of environmental factors.

Platelet monoamine oxidase type B, MAOB intron 13 and MAOA-uVNTR polymorphism and symptoms of post-traumatic stress disorder

Post-traumatic stress disorder (PTSD), a disorder that develops following exposure to traumatic experience(s), is frequently associated with agitation, aggressive behavior and psychotic symptoms. Monoamine oxidase (MAO) degrades different biogenic amines and regulates mood, emotions and behavior, and has a role in the pathophysiology of various neuropsychiatric disorders. The aim of the study was to investigate the association between different symptoms occurring in PTSD [PTSD symptom severity assessed by the Clinician Administered PTSD Scale (CAPS), agitation and selected psychotic symptoms assessed by the Positive and Negative Syndrome Scale (PANSS)] and platelet MAO-B activity and/or genetic variants of MAOB rs1799836 and MAOA-uVNTR polymorphisms in 249 Croatian male veterans with PTSD. Our study revealed slightly higher platelet MAO-B activity in veterans with PTSD with more severe PTSD symptoms and in veterans with agitation, and significantly higher platelet MAO-B activity in veterans with more pronounced psychotic symptoms compared to veterans with less pronounced psychotic symptoms. Platelet MAO-B activity was associated with smoking but not with age. Genetic variants of MAOB rs1799836 and MAOA-uVNTR were not associated with agitation and selected psychotic symptoms in veterans with PTSD. A marginally significant association was found between MAOB rs1799836 polymorphism and severity of PTSD symptoms, but it was not confirmed since carriers of G or A allele of MAOB rs1799836 did not differ in their total CAPS scores. These findings suggest an association of platelet MAO-B activity, but a lack of association of MAOB rs1799836 and MAOA-uVNTR, with selected psychotic symptoms in ethnically homogenous veterans with PTSD.

Biomarkers for attention-deficit/hyperactivity disorder (ADHD). A consensus report of the WFSBP task force on biological markers and the World Federation of ADHD

OBJECTIVE

Psychiatric "nosology" is largely based on clinical phenomenology using convention-based diagnostic systems not necessarily reflecting neurobiological pathomechanisms. While progress has been made regarding its molecular biology and neuropathology, the phenotypic characterization of ADHD has not improved. Thus, validated biomarkers, more directly linked to the underlying pathology, could constitute an objective measure for the condition.

METHOD

The task force on biological markers of the World Federation of Societies of Biological Psychiatry (WFSBP) and the World Federation of ADHD commissioned this paper to develop a consensus report on potential biomarkers of ADHD. The criteria for biomarker-candidate evaluation were: (1) sensitivity >80%, (2) specificity >80%, (3) the candidate is reliable, reproducible, inexpensive, non-invasive, easy to use, and (4) confirmed by at least two independent studies in peer-reviewed journals conducted by qualified investigators.

RESULTS

No reliable ADHD biomarker has been described to date, but some promising candidates (e.g., olfactory sensitivity, substantial echogenicity) exist. A problem in the development of ADHD markers is sample heterogeneity due to aetiological and phenotypic complexity and age-dependent co-morbidities.

CONCLUSIONS

Most likely, no single ADHD biomarker can be identified. However, the use of a combination of markers may help to reduce heterogeneity and to identify homogeneous subtypes of ADHD.

Platelet monoamine oxidase activity in children with attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a highly heritable developmental disorder characterized by symptoms of impulsivity, hyperactivity and/or inattention, and associated with structural and biochemical abnormalities in cortical and limbic structures innervated by dopamine, noradrenalin and serotonin. The enzyme monoamine oxidase, type B (MAO-B), is expressed in platelets, and metabolizes endogenous amines. Its activity has been proposed to represent a peripheral marker of various traits and forms of psychopathology. This study evaluated platelet MAO activity with a spectrofluorimetric method in 72 boys and 12 girls with predominantly hyperactive, predominantly inattentive, and combined subtype of ADHD (DSM-IV criteria), and in 64 control children. The results showed significantly lower platelet MAO activity in children with hyperactive, inattentive, and combined subtype of ADHD than in control children. There was no significant association between platelet MAO activity and gender or age. The limitation of the study was in the small sample of girls with ADHD (N=12), and in the determination of only one peripheral marker. In line with hypotheses of lower platelet MAO activity in different types of psychopathology, children with different subtypes of ADHD had significantly lower platelet MAO-B activity than control children.

Association of 5-HTT gene polymorphism, platelet MAO activity, and drive for thinness in a population-based sample of adolescent girls

OBJECTIVE

Several lines of evidence suggest that alterations in serotonergic activity contribute to the pathophysiology of abnormal eating behaviors. Since platelet monoamine oxidase (MAO) activity and the 5-HT transporter gene promoter polymorphism (5-HTTLPR) have been associated with eating disorders, the knowledge from a population-based sample may provide useful information which changes in 5-HT function observed in eating disorders represent trait vs. state effects.

METHOD

The sample was based on both cohorts of the Estonian Children Personality, Behavior and Health Study (ECPBHS). The current study was conducted during the second follow-up where altogether 82% from the original sample was recruited. EDI-2 subscales--Drive for Thinness and Bulimia--were used to determine eating attitudes and behaviors. Platelet MAO activity was measured and the participants were genotyped for the 5-HTTLPR.

RESULTS

Allelic variation of 5-HTTLPR or platelet MAO activity were not independently associated with drive for thinness or binge eating, but girls homozygous for the 5-HTTLPR long allele and with high platelet MAO activity, both considered indicators of a higher capacity 5-HT system, exhibited higher scores of drive for thinness.

CONCLUSION

The results suggest that drive for thinness is the highest in girls with the presence of two markers of higher serotonergic capacity.

Platelet MAO activity and the 5-HTT gene promoter polymorphism are associated with impulsivity and cognitive style in visual information processing

RATIONALE

Low capacity of the central serotonergic system has been associated with impulsive behaviour. Both low platelet monoamine oxidase (MAO) activity and the short (S) allele of the serotonin transporter gene promoter region polymorphism (5-HTTLPR) are proposed to be markers of less efficient serotonergic functioning.

OBJECTIVES

The effect of the two markers for serotonin system efficiency on performance in a visual comparison task (VCT) and self-reported impulsiveness (Barratt Impulsiveness Scale, BIS-11) were investigated in healthy adolescents participating in the Estonian Children Personality Behaviour and Health Study. Possible confounding effect of general cognitive abilities on the performance in VCT was controlled for.

RESULTS

Low platelet MAO activity and carrying of the S allele of 5-HTTLPR were both associated with higher error-rate and more impulsive performance in VCT. Platelet MAO activity and 5-HTTLPR S allele had a significant interactive effect on self-reported impulsivity (BIS-11). The effect of platelet MAO activity on both self-reported and performance impulsivity was significant only in the S allele carriers. The effect of 5-HTTLPR S allele on impulsive performance remained significant after controlling for general cognitive abilities.

CONCLUSIONS

The two markers of lower serotonergic capacity, 5-HTTLPR S allele and low platelet MAO activity, have a similar and partly synergistic influence on self-reported as well as performance measures of impulsivity.

Psychological traits and platelet monoamine oxidase activity in eating disorder patients: their relationship and stability

Self-reported behavior and attitudes towards eating [Eating Disorder Inventory-2; Garner DM (1991). Eating Disorder Inventory-2: Professional Manual. Odessa, Fl.: Psychological Assessment Resources; Estonian version Podar I, Hannus A, Allik J (1999). Personality and Affectivity Characteristics Associated With Eating Disorders: a Comparison of Eating Disordered, Weight-Preoccupied, and Normal Samples. J Pers Assess; 73(1), 133-147] and the activity of platelet monoamine oxidase (MAO) was studied in 11 patients with anorexia nervosa (AN), 43 patients with bulimia nervosa (BN) and a healthy control group (n=138). Nineteen patients filled in the EDI-2 questionnaire and donated blood samples three times with three month intervals in order to determine platelet MAO activity. Eating disordered (ED) patients scored higher on all EDI-2 subscales and had lower MAO activity compared to the control group. They also scored higher than the control group on the Neuroticism domain but lower on the Extraversion, Openness, and Conscientiousness domains of the NEO-PI-R questionnaire. The average stability of MAO on different occasions (r=.56) was slightly smaller than the stability of the EDI-2 scores (r=.70). The lack of correlations between personality dispositions and MAO activity indicates that they have independent influence on eating disorders. A possible relationship between neurochemical mechanisms and psychological symptoms of eating disordered behavior is discussed.

Influence of clozapine on platelet serotonin, monoamine oxidase and plasma serotonin levels

The purpose of this study was to investigate the influence of clozapine on plasma serotonin, platelet serotonin and monoamine oxidase (MAO) levels in schizophrenic patients and to compare their results with those of unmedicated healthy controls. Groups of 20 outpatients with schizophrenia and 20 healthy controls matched for age, sex and smoking status were recruited for the study. Psychopathology, neurocognitive functioning, plasma serotonin, platelet serotonin and MAO levels were assessed after 1-week drug free interval, and 8 weeks after initiation of clozapine treatment in an open design. The mean clozapine dose at week 8 was 382.5+/-96.4 (range: 250-600) mg/day. In the patient group, at baseline, plasma serotonin and platelet MAO levels were significantly lower, and platelet serotonin levels were significantly higher than in controls. After 8 weeks of clozapine treatment, plasma serotonin and platelet MAO levels increased significantly, while a significant decrease in platelet serotonin levels was detected compared with baseline values. Baseline platelet MAO levels explained 22% of the variance in Clinical Global Impression - Improvement (CGI-I) and improvement in attention, while baseline platelet serotonin predicted 23% of the variance in the improvement in positive symptoms during clozapine treatment. Our data indicate that clozapine may be reversing or compensating for a pre-existing alteration in serotonergic neurotransmission in schizophrenic patients. The prediction of response to clozapine through peripheral biochemical markers may have important clinical implications if repeated in larger samples.

Adaptive and maladaptive impulsivity, platelet monoamine oxidase (MAO) activity and risk-admitting in different types of risky drivers

RATIONALE

Platelet monoamine oxidase (MAO) activity reflects serotonergic functioning associated with impulsive behaviour, but the significance of these associations to real-life impulsive behaviour in healthy subjects is not clear.

OBJECTIVES

The present study explores impulsivity and platelet MAO activity among people with driving violations.

MATERIALS AND METHODS

We compared facets of impulsivity and platelet MAO activity in 1,004 male drivers, out of whom 203 had been caught by the police driving drunk and 292 had been caught exceeding speed limits and committing other non-alcohol-related driving violations. Subjects with speeding and other non-alcohol-related violations were further divided according to their self-reported risk-admitting of exceeding speed limits.

RESULTS

While drunk driving was associated only with maladaptive types of impulsivity, exceeding speed limits was associated with functional impulsivity and excitement seeking and, to a lesser degree, with dysfunctional impulsivity. Drunk drivers had lower platelet MAO activity. Risk-admitting high-risk drivers had higher platelet MAO activity, neuroticism-related impulsivity, dysfunctional impulsivity and excitement seeking compared to all other groups and higher functional impulsivity compared to controls. Risk-denying high-risk drivers had only higher functional impulsivity compared to controls.

CONCLUSIONS

This study demonstrates different expressions of functional and dysfunctional impulsivity in behaviour. While platelet MAO activity is lower in alcohol-related risky behaviour, non-alcohol-related self-acknowledged risky behaviour is related to higher platelet MAO activity. Thus, deviance towards lower as well as higher end of central serotonergic functioning may lead to impulsive behaviour. While self-reported impulsivity did not correlate with MAO activity, both MAO activity and impulsivity were related to risky behaviour.